Some years ago, in a Guardian review, I mentioned in passing the homosexual themes in EM Forster's fictions. I was startled to receive, by return as it were, an exceedingly sharp missive from the great man, bidding me on no account to say or write such things again. Everyone of course knew all about it, and I inferred that my real offence lay in making such a boorishly casual reference to an important mystery.

Clearly Forster liked to keep things separate. Only his own circle participated in such matters, and in the stories with a directly sexual theme, which I then knew nothing about. I think in any case my comment was misleading, for although there is an undercover element in his novels their success lies in the way in which it has been completely socialised, turned into a mastery of plot, tone, and humour. When he wrote the first study of his fiction Lionel Tulling was quite unaware of Forsters' homosexuality.

Unlike fiction today, where everything is laid on the line, his novels have an extra dimension which makes the 'faking' as Forster called it, all the livelier and more compelling. Jane Austen is a not too distant parallel. Her fiction hangs serenely over a gulf in which her fear, deprivation and resentment abide, powerless to affect it aesthetically and yet giving it their own kind of power.

Forster himself, however, appeared to equate the extra dimension with what has been rather stuffily called by critics the Fallacy of Imitative Form. In a letter to William Plomer, of 1934, a very revealing one, he remarks that in A Passage to India 'I tried to show that India is an unexplainable muddle by introducing an unexplained Muddle - Miss Quested's experience in the cave. When asked what happened there, I don't know.'

There were obvious reasons why he wouldn't. A muddled novel conveys that life is a muddle, and Plomer's novel The Invaders has, he suggests, also been 'left untidy' in order to 'show the untidiness of London.'

In a typical show of modesty Forster in fact does less than justice to A Passage to India, in which the real underlying ambiguity is about the nature of his sexual consciousness. Maybe in Plomer's case too. Forster shrugs the matter off, by writing that 'some fallacy, not a serious one, has seduced us both, some confusion between the dish and the dinner.' Since he was 'a bit old fashioned as regards form' Forster was in the odd position of taking up a stance in his novels - that of the 19th-century writer-sage like Hardy and Meredith - on which he had no intention of delivering.

Jane Austen wrote before such a stance was invented or adopted, and he could perhaps have gone on writing as she did if he had not been expected, as he told Christopher Isherwood, to 'feel advancing at this point to some Grand Pronouncement. However, it will not come.' He is not going to strike an attitude which says: 'This, this have I achieved before civilisation crashes.'

During the period of these letters Forster was in a sense 'recovering' from being a writer, whose unconscious had been hard at work. ('Dr Norman Haire has tittered to William Plomer that if my novels were analysed they would reveal a pretty mess. and that the works of H Walpole and S Maugham would be even prettier,') and was now embarking on a new life of friendship and self-discovery

Most of the letters are too hebdomadally intimate to mean much to posterity, and are intended for their correspondents rather than for the annals of literature. They have been beautifully edited, and the note are sometimes more informative than the letters themselves.